Coatings for use with contact surfaces are typically required to have superior molten metal corrosion resistance, heat resistance, thermal shock resistance, oxidation resistance, and wear resistance. Coating compositions vary depending on the specific applications, e.g., seals for gas turbine engines, sizing equipment, aircraft engine parts, forming tools, glass fiber processing parts, firearm parts (breech, a barrel, a choke, a flash suppressor, a gas port), etc. The compositions also vary depending on the function of the part or component, i.e., locking, ejection, sliding, rolling, rotating, impacting, or bearing, etc. Coating compositions in the prior art also vary depending on the final properties for the coating to impart, i.e., resistance to erosion, resistance to fretting and surface fatigue, resistance to abrasion, coating for hard bearing surfaces, coatings for soft bearing surfaces, thermal barrier or conductor, electrical insulator, abradability, low coefficient of friction or non-stick properties.
TiB2 is known to improve the fracture toughness of ceramic cutting tools and other components with a Knoop hardness of 3000 Kg/mm2 and excellent oxidation resistance for temperatures of less than 1000° C. Of all the lubricants for use in coating compositions, BN is often used to provide abradability while maintaining erosion resistance. However, in some applications, customers have to elect as whether to have the lubrication property afforded by BN, or the toughness property for a coating composition without BN or a reduced amount of BN to get the desired wear resistance.
U.S. Pat. No. 5,837,327 discloses a thermal spray/plasma spray coating composition with sintered TiB2 powder. U.S. Pat. No. 5,007,962 discloses a coating composition with BN and optionally with TiB2 being added, for use in dipping, coating, spray painting, or painting applications. U.S. Pat. No. 6,994,475 discloses bearings and a coating composition containing a solid lubricant layer comprising lubricants such as BN, graphite, or PTFE and optionally with elements such as TiB2, TiC, etc., with the optional elements being added to “impart desirable properties such as insensitivity to humidity and thermal stability.” U.S. Pat. No. 5,026,422 discloses a powder-containing composition, such as a BN-containing composition for use as a film-forming coating on substrates, wherein TiB2 powders could be added to BN powders to increase the electrical conductivity of the BN deposited coating or AlN powders could be added to BN powders to increase the thermal conductivity of the BN deposited coating.
In the manufacture of metallization boats, densified body of ceramic materials is machined into shaped articles. Cavities and/or grooves are then machined out of the shaped articles forming metallization boats. By the time metallization boats are finished according to specification, a substantial amount of scrap materials are generated. Additionally, boats not meeting specifications (for one manufacturer with >25 variables—see http://www.advceramics.com/geac/products/intermetallic_boats/), including electrical requirements and design specifications, are discarded as scrap materials as well. At the customers' site and depending on the type of boats, after a few hours in operation, some boats may begin to get corroded by molten metal with deep grooves which finally resulting in holes in the boat. At the point where there is non-uniformity in the metalized substrate due to the holes or there are holes in the boats due to metal spatter, the boats are typically replaced and discarded.
Applicants have noted that the components for use in the wear-resistant coating of the prior art are typically found in corrosion-resistant metallization boats. Applicants have also noted that scraps from corrosion-resistant metallization boats and used metallization boats are discarded in quantities, and that there are a number of applications requiring the materials typically used in metallization boats.
In one embodiment, the invention relates to a coating composition comprising a composite material with a balanced combination of low friction (lubricity) property from a material such as BN, and wear resistance (hardness) from a material such as TiB2. In a second embodiment, the invention relates to a novel and innovative way to recycle scrap materials from metallization boats and/or side dams by making useful materials out of the discarded articles, e.g., milled particles of reduced sizes in the range of 1 to 1000 microns, e.g., for use a coating composition employing a hard material such as TiB2 and a powdered solid lubricant such as BN, both components typically found in scrap materials from metallization boats and side dams.